Schizophrenia, a major psychosis that cripples the lives of patients and their families, is a brain disease in search of a neuropathological basis. Stevens (Stevens 1992; Stevens 1997) argues that a majority of patients show no signs of developmental damage, and that an uneven course after onset argues for a search for pathophysiologic processes that coincide more closely with onset, progression, or remissions, yet can explain the evidence of brain damage. She proposes that some neuropathological process that precipitates the disease (Olney and Farber 1995) is followed by waves of aberrant reinnervation and pruning. Lieberman and colleagues' (1993) five year prospective study of schizophrenia suggests that there may be a subgroup with subsequent degeneration after the onset of disease. Whatever the final resolution among these positions it seems clear that the brain lesion model that has been so successful in neuropsychology and neurology has less explanatory power in psychiatry.
Binocular rivalry is on a class of phenomena in which an unchanging but ambiguous sensory input leads to dramatic perceptual switches (Blake, 2001). If a horizontal grating is presented to the right eye and a vertical grating to the left, the usual experience by an observer is a quasi-regular, but unpredictable, switching between two mutually exclusive perceptions: a second or two of seeing only horizontal lines followed by a second or two of seeing only vertical lines (Pettigrew and Miller, 1998).
Binocular rivalry was thought to be based on the properties of monocular neurons early in the visual pathway (Blake, 1989), but recent work in monkeys trained to report their perceptual alternations has argued against this interpretation (Logothetis et al., 1996a). The present consensus is that rivalry is a multi-level process that reflects high level perceptual decisions as well as low level sensory activity (Blake, 2002).
Psychiatric interest began when bipolar patients were shown to have a significantly slower perceptual alternation rate, independent of age and medication (Pettigrew and Miller, 1998; International patent publication WO 99/63889, incorporated herein by reference). The altered neural rhythm revealed by binocular rivalry in bipolar patients is also accompanied by alteration of another of their neural rhythms with a period of hours rather than seconds. Considered along with the evidence that the switches of rivalry reflect interhemispheric switching, (Miller et al., 2000), the neural dysrhythmia in bipolar disorder revealed by binocular rivalry may be related to abnormal regulation of the hemispheric asymmetries of mood. Perceptual rivalry may therefore play a role in explaining bipolar disorder as well as in diagnosing it.
A method and apparatus capable of diagnosing a bipolar disorder, is described in WO 99/63889. The method includes the steps of determining an interhemispheric switch rate of a test subject and comparing the switch rate with a corresponding reference switch rate to diagnose presence or absence of a bipolar disorder or predisposition thereto. The apparatus provides a means for measuring a rate of standard binocular rivalry in a test subject.
Dichoptic alternation during binocular rivalry was first described by Logothetis and Leopold (1996) in normal subjects. If complementary patterns being presented to each eye to produce rivalry are swapped, normal subjects continue to show slow perceptual alternations (every few seconds), even though the stimuli are changing much more rapidly at each eye (2-3 Hz). At high rates of dichoptic alternation, a normal individual sees both patterns simultaneously instead of alternating.
Early diagnosis is important in relation to treatment and prevention of schizophrenia. However, this effort is hampered by the fact that psychiatric diagnosis is currently difficult and inaccurate. For example, between 50-70% of “first break” psychoses in young adults called “schizophrenia” are subsequently shown to be misdiagnosed.
There is a need for a simple objective method of diagnosing schizophrenia. It is apparent that this disorder is heterogeneous, so a subtype identification method could be useful in subsequent management as well as understanding of the condition.